It is your supposition that it was 'concocted'. You have no way of knowing whether it was a genuinely held belief or otherwise.
Anyone with a modicum of common sense, gumption and deduction abilities can see the sheer ludicrousness of the proposition that there was someone hiding in the kids wardrobe when Gerry was there and subsequently darted out within 2-3 minutes in full view across the very road the child's father was stood in and talking on.
Using those same assets one can deduce, given this detail was added much later that it was simply created in order to facilitate a window of opportunity.
Says who? You? How do you know what the Oporto Inquiry or the SY Investigation are thinking?
We know they have ruled out the 9:15 sighting which indicates an abduction nearer the time of the Smiths sighting at 10:00. We also know the distance is around 5 minutes from 5A to the Smiths sighting. This leads to an abduction around 9:50-9:55. Why would an abductor need to hide in a wardrobe when no one was in the apartment from 9:30 until 10:00?
Presumptions on anyone's part can be wrong. And alternatives may actually be true.
Presumptions, in order to carry weight, have to be based on "known knowns". See above on what we now know about an abduction window.
Now you can presume that an abductor hid in the parents bedroom, but what facts we have from the files and from SY's comments offer no reason or logic why this abductor should need to hide in any wardrobe but particularly the wardrobe in the parents bedroom, when he came to abduct a child from the other bedroom.
You can presume that aliens abducted Madeleine, but there are no facts or logic in the supporting material and information which support that presumption.
Much like the idea an abductor who happens to have cadaver scent on his personage who hid in the wardrobe of the bedroom which did not contain the child he came to abduct, to hide from the child's parents who, in the time frame of the abduction, were not in the apartment and he had no need to hide from.
He may have opened the doors and pulled them close towards him while remaining standing. Not a very effective cover but in an emergency perhaps the best he could find.
Also there is the statement by Grime about the alerts in the apartment in which he suggests that the location may not be accurate as the cadaver odour could have pooled in a particular place due to air currents.
Nothing should be ruled out just because amateurs like you or me simply can't see how it fits. These things are best left to the professionals in my view.
I repeat the scenario presented by SY, which you appear to have so much truck with - indeed having built and populated this thread espousing its virtue and veracity - indicates the abduction happened much later than 9:15 during a period when no one was in the apartment. Why play hide and seek in a wardrobe to hide from people who were not there?
In relation to Grime's comments it is noticeable and not entirely coincidental that these air currents and transferal of cadaver odour only appear to have happened in 5A and nowhere else.
How odd.